x86,objtool: Split UNWIND_HINT_EMPTY in two

Mark reported that the ORC unwinder incorrectly marks an unwind as
reliable when the unwind terminates prematurely in the dark corners of
return_to_handler() due to lack of information about the next frame.

The problem is UNWIND_HINT_EMPTY is used in two different situations:

1) The end of the kernel stack unwind before hitting user entry, boot
code, or fork entry

2) A blind spot in ORC coverage where the unwinder has to bail due to
lack of information about the next frame

The ORC unwinder has no way to tell the difference between the two.
When it encounters an undefined stack state with 'end=1', it blindly
marks the stack reliable, which can break the livepatch consistency
model.

Fix it by splitting UNWIND_HINT_EMPTY into UNWIND_HINT_UNDEFINED and
UNWIND_HINT_END_OF_STACK.

Reported-by: Mark Rutland <[e-mail]>
Signed-off-by: Josh Poimboeuf <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Acked-by: Steven Rostedt (Google) <[e-mail]>
Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/livepatch/reliable-stacktrace.rst

···
 .. code-block:: none
 
    SYM_CODE_START(return_to_handler)
-           UNWIND_HINT_EMPTY
+           UNWIND_HINT_UNDEFINED
            subq  $24, %rsp
 
            /* Save the return values */

arch/x86/entry/entry_64.S

···
 	 */
 	movq	%rsp, %rdi
 	movq	PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 
 	pushq	RSP-RDI(%rdi)	/* RSP */
 	pushq	(%rdi)		/* RDI */
···
 .pushsection .text, "ax"
 	__FUNC_ALIGN
 SYM_CODE_START_NOALIGN(ret_from_fork)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR // copy_thread
 	CALL_DEPTH_ACCOUNT
 	movq	%rax, %rdi
···
 
 1:
 	/* kernel thread */
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	movq	%r12, %rdi
 	CALL_NOSPEC rbx
 	/*
···
 	 */
 	movq	%rsp, %rdi
 	movq	PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 
 	/* Copy the IRET frame to the trampoline stack. */
 	pushq	6*8(%rdi)	/* SS */
···
  */
 	__FUNC_ALIGN
 SYM_CODE_START_NOALIGN(xen_failsafe_callback)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_UNDEFINED
 	ENDBR
 	movl	%ds, %ecx
 	cmpw	%cx, 0x10(%rsp)
···
  * MSRs to fully disable 32-bit SYSCALL.
  */
 SYM_CODE_START(ignore_sysret)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ENDBR
 	mov	$-ENOSYS, %eax
 	sysretl

arch/x86/include/asm/orc_types.h

···
 #define ORC_REG_SP_INDIRECT		9
 #define ORC_REG_MAX			15
 
-#define ORC_TYPE_CALL			0
-#define ORC_TYPE_REGS			1
-#define ORC_TYPE_REGS_PARTIAL		2
+#define ORC_TYPE_UNDEFINED		0
+#define ORC_TYPE_END_OF_STACK		1
+#define ORC_TYPE_CALL			2
+#define ORC_TYPE_REGS			3
+#define ORC_TYPE_REGS_PARTIAL		4
 
 #ifndef __ASSEMBLY__
 #include <asm/byteorder.h>
···
 #if defined(__LITTLE_ENDIAN_BITFIELD)
 	unsigned	sp_reg:4;
 	unsigned	bp_reg:4;
-	unsigned	type:2;
+	unsigned	type:3;
 	unsigned	signal:1;
-	unsigned	end:1;
 #elif defined(__BIG_ENDIAN_BITFIELD)
 	unsigned	bp_reg:4;
 	unsigned	sp_reg:4;
 	unsigned	unused:4;
-	unsigned	end:1;
 	unsigned	signal:1;
-	unsigned	type:2;
+	unsigned	type:3;
 #endif
 } __packed;
 

arch/x86/include/asm/unwind_hints.h

···
 
 #ifdef __ASSEMBLY__
 
-.macro UNWIND_HINT_EMPTY
-	UNWIND_HINT type=UNWIND_HINT_TYPE_CALL end=1
+.macro UNWIND_HINT_END_OF_STACK
+	UNWIND_HINT type=UNWIND_HINT_TYPE_END_OF_STACK
+.endm
+
+.macro UNWIND_HINT_UNDEFINED
+	UNWIND_HINT type=UNWIND_HINT_TYPE_UNDEFINED
 .endm
 
 .macro UNWIND_HINT_ENTRY
 	VALIDATE_UNRET_BEGIN
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 .endm
 
 .macro UNWIND_HINT_REGS base=%rsp offset=0 indirect=0 extra=1 partial=0 signal=1
···
 #else
 
 #define UNWIND_HINT_FUNC \
-	UNWIND_HINT(UNWIND_HINT_TYPE_FUNC, ORC_REG_SP, 8, 0, 0)
+	UNWIND_HINT(UNWIND_HINT_TYPE_FUNC, ORC_REG_SP, 8, 0)
 
 #endif /* __ASSEMBLY__ */
 

arch/x86/kernel/ftrace_64.S

···
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 SYM_CODE_START(return_to_handler)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_UNDEFINED
 	ANNOTATE_NOENDBR
 	subq  $16, %rsp
 

arch/x86/kernel/head_64.S

···
 	__HEAD
 	.code64
 SYM_CODE_START_NOALIGN(startup_64)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	/*
 	 * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
 	 * and someone has loaded an identity mapped page table
···
 	lretq
 
 .Lon_kernel_cs:
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 
 	/* Sanitize CPU configuration */
 	call verify_cpu
···
 SYM_CODE_END(startup_64)
 
 SYM_CODE_START(secondary_startup_64)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR
 	/*
 	 * At this point the CPU runs in 64bit mode CS.L = 1 CS.D = 0,
···
 	 * verify_cpu() above to make sure NX is enabled.
 	 */
 SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR
 
 	/*
···
 	ANNOTATE_RETPOLINE_SAFE
 	jmp	*%rax
 1:
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR // above
 
 	/*
···
  */
 SYM_CODE_START(start_cpu0)
 	ANNOTATE_NOENDBR
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	movq	initial_stack(%rip), %rsp
 	jmp	.Ljump_to_C_code
 SYM_CODE_END(start_cpu0)

arch/x86/kernel/relocate_kernel_64.S

···
 	.code64
 SYM_CODE_START_NOALIGN(relocate_range)
 SYM_CODE_START_NOALIGN(relocate_kernel)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR
 	/*
 	 * %rdi indirection_page
···
 SYM_CODE_END(relocate_kernel)
 
 SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	/* set return address to 0 if not preserving context */
 	pushq	$0
 	/* store the start address on the stack */
···
 SYM_CODE_END(identity_mapped)
 
 SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR // RET target, above
 	movq	RSP(%r8), %rsp
 	movq	CR4(%r8), %rax
···
 
 	/* Do the copies */
 SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
-	UNWIND_HINT_EMPTY
-	movq	%rdi, %rcx 	/* Put the page_list in %rcx */
+	UNWIND_HINT_END_OF_STACK
+	movq	%rdi, %rcx	/* Put the page_list in %rcx */
 	xorl	%edi, %edi
 	xorl	%esi, %esi
 	jmp	1f

arch/x86/kernel/unwind_orc.c

···
 	.sp_offset	= 16,
 	.bp_reg		= ORC_REG_PREV_SP,
 	.bp_offset	= -16,
-	.end		= 0,
 };
 
 static struct orc_entry *orc_find(unsigned long ip)
···
 		return -1;
 
 	/*
-	 * The "weak" section terminator entries need to always be on the left
+	 * The "weak" section terminator entries need to always be first
 	 * to ensure the lookup code skips them in favor of real entries.
 	 * These terminator entries exist to handle any gaps created by
 	 * whitelisted .o files which didn't get objtool generation.
 	 */
 	orc_a = cur_orc_table + (a - cur_orc_ip_table);
-	return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1;
+	return orc_a->type == ORC_TYPE_UNDEFINED ? -1 : 1;
 }
 
 void unwind_module_init(struct module *mod, void *_orc_ip, size_t orc_ip_size,
···
 		 */
 		orc = &orc_fp_entry;
 		state->error = true;
-	}
-
-	/* End-of-stack check for kernel threads: */
-	if (orc->sp_reg == ORC_REG_UNDEFINED) {
-		if (!orc->end)
+	} else {
+		if (orc->type == ORC_TYPE_UNDEFINED)
 			goto err;
 
-		goto the_end;
+		if (orc->type == ORC_TYPE_END_OF_STACK)
+			goto the_end;
 	}
 
 	state->signal = orc->signal;

arch/x86/lib/retpoline.S

···
 
 	.align RETPOLINE_THUNK_SIZE
 SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_UNDEFINED
 	ANNOTATE_NOENDBR
 
 	ALTERNATIVE_2 __stringify(RETPOLINE \reg), \
···
 	.align RETPOLINE_THUNK_SIZE
 
 SYM_INNER_LABEL(__x86_indirect_call_thunk_\reg, SYM_L_GLOBAL)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_UNDEFINED
 	ANNOTATE_NOENDBR
 
 	CALL_DEPTH_ACCOUNT
···
 	.align RETPOLINE_THUNK_SIZE
 
 SYM_INNER_LABEL(__x86_indirect_jump_thunk_\reg, SYM_L_GLOBAL)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_UNDEFINED
 	ANNOTATE_NOENDBR
 	POLINE \reg
 	ANNOTATE_UNRET_SAFE

arch/x86/platform/pvh/head.S

···
 #define PVH_DS_SEL		(PVH_GDT_ENTRY_DS * 8)
 
 SYM_CODE_START_LOCAL(pvh_start_xen)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	cld
 
 	lgdt (_pa(gdt))

arch/x86/xen/xen-asm.S

···
 SYM_CODE_START(xen_early_idt_handler_array)
 	i = 0
 	.rept NUM_EXCEPTION_VECTORS
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_UNDEFINED
 	ENDBR
 	pop %rcx
 	pop %r11
···
  * rsp->rax		}
  */
 SYM_CODE_START(xen_iret)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_UNDEFINED
 	ANNOTATE_NOENDBR
 	pushq $0
 	jmp hypercall_iret

arch/x86/xen/xen-head.S

···
 #ifdef CONFIG_XEN_PV
 	__INIT
 SYM_CODE_START(startup_xen)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR
 	cld
 
···
 #ifdef CONFIG_XEN_PV_SMP
 .pushsection .text
 SYM_CODE_START(asm_cpu_bringup_and_idle)
-	UNWIND_HINT_EMPTY
+	UNWIND_HINT_END_OF_STACK
 	ENDBR
 
 	call cpu_bringup_and_idle

include/linux/objtool.h

···
 
 #ifndef __ASSEMBLY__
 
-#define UNWIND_HINT(type, sp_reg, sp_offset, signal, end)	\
+#define UNWIND_HINT(type, sp_reg, sp_offset, signal)	\
 	"987: \n\t"						\
 	".pushsection .discard.unwind_hints\n\t"		\
 	/* struct unwind_hint */				\
···
 	".byte " __stringify(sp_reg) "\n\t"			\
 	".byte " __stringify(type) "\n\t"			\
 	".byte " __stringify(signal) "\n\t"			\
-	".byte " __stringify(end) "\n\t"			\
 	".balign 4 \n\t"					\
 	".popsection\n\t"
 
···
  * the debuginfo as necessary.  It will also warn if it sees any
  * inconsistencies.
  */
-.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0 end=0
+.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0
 .Lhere_\@:
 	.pushsection .discard.unwind_hints
 		/* struct unwind_hint */
···
 		.byte \sp_reg
 		.byte \type
 		.byte \signal
-		.byte \end
 		.balign 4
 	.popsection
 .endm
···
 
 #ifndef __ASSEMBLY__
 
-#define UNWIND_HINT(type, sp_reg, sp_offset, signal, end) "\n\t"
+#define UNWIND_HINT(type, sp_reg, sp_offset, signal) "\n\t"
 #define STACK_FRAME_NON_STANDARD(func)
 #define STACK_FRAME_NON_STANDARD_FP(func)
 #define ANNOTATE_NOENDBR
 #define ASM_REACHABLE
 #else
 #define ANNOTATE_INTRA_FUNCTION_CALL
-.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0 end=0
+.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0
 .endm
 .macro STACK_FRAME_NON_STANDARD func:req
 .endm

include/linux/objtool_types.h

···
 	u8		sp_reg;
 	u8		type;
 	u8		signal;
-	u8		end;
 };
 
 #endif /* __ASSEMBLY__ */
 
 /*
+ * UNWIND_HINT_TYPE_UNDEFINED: A blind spot in ORC coverage which can result in
+ * a truncated and unreliable stack unwind.
+ *
+ * UNWIND_HINT_TYPE_END_OF_STACK: The end of the kernel stack unwind before
+ * hitting user entry, boot code, or fork entry (when there are no pt_regs
+ * available).
+ *
  * UNWIND_HINT_TYPE_CALL: Indicates that sp_reg+sp_offset resolves to PREV_SP
  * (the caller's SP right before it made the call).  Used for all callable
  * functions, i.e. all C code and all callable asm functions.
···
  * UNWIND_HINT_TYPE_REGS_PARTIAL: Used in entry code to indicate that
  * sp_reg+sp_offset points to the iret return frame.
  *
- * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
+ * UNWIND_HINT_TYPE_FUNC: Generate the unwind metadata of a callable function.
  * Useful for code which doesn't have an ELF function annotation.
  *
- * UNWIND_HINT_ENTRY: machine entry without stack, SYSCALL/SYSENTER etc.
+ * UNWIND_HINT_TYPE_{SAVE,RESTORE}: Save the unwind metadata at a certain
+ * location so that it can be restored later.
  */
-#define UNWIND_HINT_TYPE_CALL		0
-#define UNWIND_HINT_TYPE_REGS		1
-#define UNWIND_HINT_TYPE_REGS_PARTIAL	2
+#define UNWIND_HINT_TYPE_UNDEFINED	0
+#define UNWIND_HINT_TYPE_END_OF_STACK	1
+#define UNWIND_HINT_TYPE_CALL		2
+#define UNWIND_HINT_TYPE_REGS		3
+#define UNWIND_HINT_TYPE_REGS_PARTIAL	4
 /* The below hint types don't have corresponding ORC types */
-#define UNWIND_HINT_TYPE_FUNC		3
-#define UNWIND_HINT_TYPE_SAVE		4
-#define UNWIND_HINT_TYPE_RESTORE	5
+#define UNWIND_HINT_TYPE_FUNC		5
+#define UNWIND_HINT_TYPE_SAVE		6
+#define UNWIND_HINT_TYPE_RESTORE	7
 
 #endif /* _LINUX_OBJTOOL_TYPES_H */

scripts/sorttable.h

···
 	 * whitelisted .o files which didn't get objtool generation.
 	 */
 	orc_a = g_orc_table + (a - g_orc_ip_table);
-	return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1;
+	return orc_a->type == ORC_TYPE_UNDEFINED ? -1 : 1;
 }
 
 static void *sort_orctable(void *arg)

tools/arch/x86/include/asm/orc_types.h

···
 #define ORC_REG_SP_INDIRECT		9
 #define ORC_REG_MAX			15
 
-#define ORC_TYPE_CALL			0
-#define ORC_TYPE_REGS			1
-#define ORC_TYPE_REGS_PARTIAL		2
+#define ORC_TYPE_UNDEFINED		0
+#define ORC_TYPE_END_OF_STACK		1
+#define ORC_TYPE_CALL			2
+#define ORC_TYPE_REGS			3
+#define ORC_TYPE_REGS_PARTIAL		4
 
 #ifndef __ASSEMBLY__
 #include <asm/byteorder.h>
···
 #if defined(__LITTLE_ENDIAN_BITFIELD)
 	unsigned	sp_reg:4;
 	unsigned	bp_reg:4;
-	unsigned	type:2;
+	unsigned	type:3;
 	unsigned	signal:1;
-	unsigned	end:1;
 #elif defined(__BIG_ENDIAN_BITFIELD)
 	unsigned	bp_reg:4;
 	unsigned	sp_reg:4;
 	unsigned	unused:4;
-	unsigned	end:1;
 	unsigned	signal:1;
-	unsigned	type:2;
+	unsigned	type:3;
 #endif
 } __packed;
 

tools/include/linux/objtool_types.h

···
 	u8		sp_reg;
 	u8		type;
 	u8		signal;
-	u8		end;
 };
 
 #endif /* __ASSEMBLY__ */
 
 /*
+ * UNWIND_HINT_TYPE_UNDEFINED: A blind spot in ORC coverage which can result in
+ * a truncated and unreliable stack unwind.
+ *
+ * UNWIND_HINT_TYPE_END_OF_STACK: The end of the kernel stack unwind before
+ * hitting user entry, boot code, or fork entry (when there are no pt_regs
+ * available).
+ *
  * UNWIND_HINT_TYPE_CALL: Indicates that sp_reg+sp_offset resolves to PREV_SP
  * (the caller's SP right before it made the call).  Used for all callable
  * functions, i.e. all C code and all callable asm functions.
···
  * UNWIND_HINT_TYPE_REGS_PARTIAL: Used in entry code to indicate that
  * sp_reg+sp_offset points to the iret return frame.
  *
- * UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
+ * UNWIND_HINT_TYPE_FUNC: Generate the unwind metadata of a callable function.
  * Useful for code which doesn't have an ELF function annotation.
  *
- * UNWIND_HINT_ENTRY: machine entry without stack, SYSCALL/SYSENTER etc.
+ * UNWIND_HINT_TYPE_{SAVE,RESTORE}: Save the unwind metadata at a certain
+ * location so that it can be restored later.
  */
-#define UNWIND_HINT_TYPE_CALL		0
-#define UNWIND_HINT_TYPE_REGS		1
-#define UNWIND_HINT_TYPE_REGS_PARTIAL	2
+#define UNWIND_HINT_TYPE_UNDEFINED	0
+#define UNWIND_HINT_TYPE_END_OF_STACK	1
+#define UNWIND_HINT_TYPE_CALL		2
+#define UNWIND_HINT_TYPE_REGS		3
+#define UNWIND_HINT_TYPE_REGS_PARTIAL	4
 /* The below hint types don't have corresponding ORC types */
-#define UNWIND_HINT_TYPE_FUNC		3
-#define UNWIND_HINT_TYPE_SAVE		4
-#define UNWIND_HINT_TYPE_RESTORE	5
+#define UNWIND_HINT_TYPE_FUNC		5
+#define UNWIND_HINT_TYPE_SAVE		6
+#define UNWIND_HINT_TYPE_RESTORE	7
 
 #endif /* _LINUX_OBJTOOL_TYPES_H */

tools/objtool/check.c

···
 	memcpy(&state->regs, &initial_func_cfi.regs,
 	       CFI_NUM_REGS * sizeof(struct cfi_reg));
 	state->stack_size = initial_func_cfi.cfa.offset;
+	state->type = UNWIND_HINT_TYPE_CALL;
 }
 
 static int read_unwind_hints(struct objtool_file *file)
···
 		cfi.cfa.offset = bswap_if_needed(file->elf, hint->sp_offset);
 		cfi.type = hint->type;
 		cfi.signal = hint->signal;
-		cfi.end = hint->end;
 
 		insn->cfi = cfi_hash_find_or_add(&cfi);
 	}

tools/objtool/orc_dump.c

···
 static const char *orc_type_name(unsigned int type)
 {
 	switch (type) {
+	case ORC_TYPE_UNDEFINED:
+		return "(und)";
+	case ORC_TYPE_END_OF_STACK:
+		return "end";
 	case ORC_TYPE_CALL:
 		return "call";
 	case ORC_TYPE_REGS:
···
 			printf("%llx:", (unsigned long long)(orc_ip_addr + (i * sizeof(int)) + orc_ip[i]));
 		}
 
+		printf("type:%s", orc_type_name(orc[i].type));
 
 		printf(" sp:");
 
···
 
 		print_reg(orc[i].bp_reg, bswap_if_needed(&dummy_elf, orc[i].bp_offset));
 
-		printf(" type:%s signal:%d end:%d\n",
-		       orc_type_name(orc[i].type), orc[i].signal, orc[i].end);
+		printf(" signal:%d\n", orc[i].signal);
 	}
 
 	elf_end(elf);

tools/objtool/orc_gen.c

···
 	memset(orc, 0, sizeof(*orc));
 
 	if (!cfi) {
-		orc->end = 0;
-		orc->sp_reg = ORC_REG_UNDEFINED;
+		/*
+		 * This is usually either unreachable nops/traps (which don't
+		 * trigger unreachable instruction warnings), or
+		 * STACK_FRAME_NON_STANDARD functions.
+		 */
+		orc->type = ORC_TYPE_UNDEFINED;
 		return 0;
 	}
 
 	switch (cfi->type) {
+	case UNWIND_HINT_TYPE_UNDEFINED:
+		orc->type = ORC_TYPE_UNDEFINED;
+		return 0;
+	case UNWIND_HINT_TYPE_END_OF_STACK:
+		orc->type = ORC_TYPE_END_OF_STACK;
+		return 0;
 	case UNWIND_HINT_TYPE_CALL:
 		orc->type = ORC_TYPE_CALL;
 		break;
···
 		return -1;
 	}
 
-	orc->end = cfi->end;
 	orc->signal = cfi->signal;
-
-	if (cfi->cfa.base == CFI_UNDEFINED) {
-		orc->sp_reg = ORC_REG_UNDEFINED;
-		return 0;
-	}
 
 	switch (cfi->cfa.base) {
 	case CFI_SP:
···
 	struct orc_list_entry *entry;
 	struct list_head orc_list;
 
-	struct orc_entry null = {
-		.sp_reg  = ORC_REG_UNDEFINED,
-		.bp_reg  = ORC_REG_UNDEFINED,
-		.type    = ORC_TYPE_CALL,
-	};
+	struct orc_entry null = { .type = ORC_TYPE_UNDEFINED };
 
 	/* Build a deduplicated list of ORC entries: */
 	INIT_LIST_HEAD(&orc_list);